This invention relates to a directed energy beam system.
From a 1996 press release from Los Alamos National Laboratory titled, xe2x80x9cThere""s new light at the end of the tunnel for some laser-based technologiesxe2x80x9d:
xe2x80x9cResearchers Xin Miao Zhao, David Funk, Charlie Strauss, Toni Taylor and Jason Jones experimenting with a powerful infrared titanium-sapphire laser found that when a light pulse intensity reaches a critical value, the beam focuses itself into a thin filament without the aid of focusing lenses or mirrors and perpetuates itself for long distances.
The beamxe2x80x94two to three times the thickness of a human hairxe2x80x94propagates virtually indefinitely through air without spreading, something conventional lasers cannot do.xe2x80x9d
U.S. Pat. No. 5,726,855 APPARATUS AND METHOD FOR ENABLING THE CREATION OF MULTIPLE EXTENDED CONDUCTION PATHS IN THE ATMOSPHERE, issued Mar. 10, 1998 to Mourou et al. teaches a method for enabling the creation of multiple extended conduction paths in the atmosphere through the use of a chirped-pulse amplification laser system having a high peak-power laser capable of transmitting through the atmosphere a high-peak power ultrashort laser pulse.
The creation of the conduction path is described in Column 4, line 50 through Column 5, line 22:
xe2x80x9cFor a high peak-power ultrashort pulse, the peak-power can be strong enough to drive the electrons of the material it is propagating through their linear regime and into a nonlinear regime. In this case, the index of refraction for the material can be written n(r)=n.sub.0+n.sub.2 I(r), where n(r) is the radially varying index of refraction, n.sub.o is the linear (standard) index of refraction, n.sub.2 is the nonlinear refractive index, and I(r) is the radially varying intensity. Since the center of the beam has a higher intensity than the outer edges, the index of refraction varies radially (just as in a regular glass lens), and the pulse experiences a positive lensing effect, even if it is collimated at low powers. This is called self-focusing. The critical peak-power needed to start self-focusing is given by Pcr=.lambda.. sup.2/(2.pi.n.sub.2) which for air is 1.8.times.10.sup.9 W but has been measured to be more like 1.times.10.sup.10 W. With an initially smooth spacial beam, only one filament appears at the center of the beam. Once the beam (or part of it) self-focuses, it will not focus to an arbitrarily small size. It will self-focus until the intensity of the pulse is large enough to ionize the material. This generated plasma reduces the on-axis index of refraction by an amount given by 4.pi.e.sup.2 n.sub.e (I)/(2m.sub.e omega.. sup.2) where n.sub.e (I) is the intensity dependent generated plasma density, e is the electron charge, m.sub.e is the electron mass, and omega. is the laser frequency. Again, the beam experiences a radially varying index of refraction change (because n.sub.e (I) is radially varying) and the change due to the plasma acts as a negative (defocusing) lens. So, through the balance of the continual self-focusing (positive lens) and the plasma defocusing and natural diffraction (negative lens), the pulse stays confined to a high-intensity, small diameter over many meters of propagation while automatically producing free electrons. This is a xe2x80x98naturalxe2x80x99 way of generating an extended plasma channel. The only preparation needed from the user is to generate the high peak-power laser pulse.
Each self-focused xe2x80x9chotspotxe2x80x9d creates one electrically conductive ionized channel or plasma column in the atmosphere. The plasma columns can be used for many different applications, one such application being to safely and repetitively control the discharge of lightning strikes before natural breakdown occurs to protect power plants, airports, launch sites, etc.xe2x80x9d
Hardric Laboratories, Inc. of North Chelmsford, Mass., produces mirrors made of bare-polished beryllium metal that produce a high level of reflectivity.
The world is a hostile place. In recent years there has been a proliferation of countries with strategic and tactical ballistic missiles and cruise missiles capable of delivering nuclear, biological, and chemical weapons. The methods used to combat these threats fall into two categories: Lasers and Anti-Missile Missiles (AMM).
An example of the first category is the Airborne Laser (ABL) which uses a high-power chemical laser and is carried in a 747 aircraft. Because it uses a chemical laser it can fire only a limited number of times before the chemicals are used up. In addition, its use in a 747 makes it vulnerable to being shot down.
In the category of Anti-Missile Missiles, all systems share the disadvantage that an AMM, however fast, takes time to reach the target. This reduces the time available for finding and identifying it as a threat. It also makes second shots less possible.
Accordingly, one of the objects and advantages of my invention is to provide a new method of providing a defense against ballistic missiles and cruise missiles.
Further objects and advantages of my invention will become apparant from a consideration of the drawings and ensuing description.
A laser system, such as the one taught by Mourou et al. is used to produce a thin ionizing beam through the atmosphere. The thin ionizing beam, or plasma beam, is electrically conducting and is moved in either a circular or rectangular fashion to produce a conductive shell to act as a waveguide for microwave energy. Since the waveguide is composed of a plasma it is called a plasma beam waveguide.
In a first embodiment the plasma beam waveguide is formed by physically moving the laser system used to produce the beam. Microwave energy is coupled into the plasma beam waveguide through a hole in the laser assembly.
In a second embodiment the laser system is stationary and the beam is moved by using a parabolic mirror with an offset feed. A flat mirror, using a mirror positioner having either one or two degrees of freedom, is mounted at the feedpoint and is used to reflect the laser beam around the periphery of the parabolic mirror, producing a shell. Microwave energy is coupled into the plasma beam waveguide through a hole in the center of the parabolic mirror. This is the reason for using a parabolic mirror with an offset feed.
In a third embodiment the laser system is also stationary and the beam is moved by using a parabolic mirror with an offset feed. However, the beam is electrically accelerated and then magnetically deflected by an orthogonal pair of electromagnetic coils at the feedpoint. The plasma beam is electrically accelerated by inducing a current in the plasma beam between two conducting mirrors. To accomplish this, both mirrors are made of a conducting material such as beryllium metal, and a current source is connected between them.
In all three embodiments the entire assembly can be mounted on a standard azimuth-elevation mount to allow the system to be aimed.
Since microwave energy can be produced more efficiently than laser energy, this system can be used to deliver a directed beam of energy more efficiently than a laser acting alone.
At high power levels the directed energy beam system can be used as a weapon. Because the system operates soley from electricity it is easily scaled by adding more units. Therefore its use as a defense weapon has an advantage over its use as an offensive weapon.
Another use at high power levels is to power the first stage of a rocket booster. A number of directed energy beam systems are arranged to direct their energy beams at a rocket booster whose fuel consists of water. The microwave energy is used to superheat the water which is then directed through a conventional rocket engine nozzle. The use of water as a fuel eliminates the toxicity problems of conventional rocket fuels. Water is also less expensive and more easily stored than conventional rocket fuels.
At moderate power levels the directed energy beam system can be used to provide power to an unmanned aerial vehicle (UAV), enabling the UAV to remain on-station for extended periods of time.
Because an object interrupting a waveguide produces a discontinuity in waveguide impedance which is reflected back to the source this system can also be used to track the UAV to maintain beam position.
Where it is not necessary to transmit appreciable amounts of power, the directed energy beam system can be used as an ultra-precise radar system.